protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                Map1.MapUnit = GeographyUnit.DecimalDegree;
                Map1.CurrentExtent = new RectangleShape(-180, 92.0859375, 180, -93.5390625);
                Map1.MapBackground.BackgroundBrush = new GeoSolidBrush(GeoColor.GeographicColors.ShallowOcean);
                SimpleMarkerOverlay markerOverlay = new SimpleMarkerOverlay("MarkerOverlay");
                markerOverlay.Markers.Add(new Marker(-0, 0, new WebImage(21, 25, -10.5f, -25f)));
                Map1.CustomOverlays.Add(markerOverlay);
            }
        }

        void Map1_ExtentChanged(object sender, ExtentChangedEventArgs e)
        {
            if (e.CurrentScale == Map1.ZoomLevelSet.ZoomLevel19.Scale)
            {
                (Map1.CustomOverlays[0] as SimpleMarkerOverlay).Markers[0].IsVisible = false;
            }
        }